The present invention generally relates to heat exchange apparatus and, in a preferred embodiment thereof, more particularly relates to an air conditioning unit, such as an outdoor condensing unit, having incorporated therein a coil portion with a specially designed non-uniform fin arrangement.
The coil portion of an air conditioning unit, such as an outside condensing unit, is typically made up of parallel tubing sections through which refrigerant is flowed, and a series of parallel, thin fin members transversely secured to the tubing sections in a closely spaced arrangement. Conventionally, the number of fins per inch (FPI) is kept constant over the entire face area of the coil. To force air through the fin spaces and externally across the tubing sections a fan structure is typically employed. Due to the placement of the fan structure relative to the coil it is common for the coil to have on different areas thereof substantially different face velocities of air traversing it.
This nonuniform air velocity through different portions of the coil often creates a variety of operational problems and inefficiencies for the air conditioning unit in which the coil is incorporated, including making condensate drainage difficult, increasing the possibility for icing up of certain coil portions, and lowering the overall heat exchange capability of the coil. It is to these problems that the present invention is directed.
In carrying out principles of the present invention, in accordance with a preferred embodiment thereof, heat exchange apparatus is provided which is representatively in the form of an outdoor condensing unit portion of a direct expansion air conditioning system.
From a broad perspective the heat exchange apparatus comprises a heat transfer coil including a plurality of parallel tube sections laterally spaced apart in a first direction and through which a fluid may be flowed, and a mutually spaced series of parallel fin members transversely secured to the tube sections. The heat exchange apparatus also comprises fan apparatus associated with the heat transfer coil and operative to flow air therethrough, between the fin members and externally across the tube sections, in an air flow direction.
According to one aspect of the invention, the fin members have major dimensions which extend generally parallel to the first direction, the major dimensions varying generally transversely to the air flow direction and generally parallel to the first direction. According to another aspect of the invention, the air-to-fin contact area of the heat transfer coil varies generally transversely to the air flow direction and generally parallel to the fins and the first direction. Other features of the invention include, in various combinations with these aspects, that the air flow direction across the coil is generally transverse to the first direction, the fin spacing is substantially uniform, and that the thicknesses of the fins are substantially uniform.
AS representatively embodied in an outdoor condensing unit, the invention provides a generally vertically oriented coil in which the parallel tube sections are laterally spaced apart in a vertical direction, and the fins are transversely secured to the tube sections. Fins which extend from the top of the coil to the bottom of the coil are horizontally interdigitated with shorter fins which extend from the top of the coil to a location which is spaced upwardly apart from the bottom of the coil. In this manner, the fin density and air-to-fin contact area along a bottom portion of the coil are substantially reduced relative to the fin density and air-to-fin contact area along an upper portion of the coil.
During operation of the fan, ambient outside air is flowed generally horizontally inwardly through the coil into the interior of the condensing unit, thereby receiving heat from the coil, and then vertically discharged from the condensing unit. The lowered fin density in the bottom portion of the coil reduces the air pressure drop across such bottom portion and provides the condensing unit with a variety of advantages over condensing units having conventionally configured fin/tube coils, such advantages including material cost savings, weight reduction, enhanced air side convective heat transfer, improved air velocity profiles, lowered air side pressure drop, improved condensate drainage efficiency, lowered frost and ice accumulation on the coil, lowered thermal coil stress, and easier cleaning of the bottom coil portion.
While the present invention is illustrated and described herein as being incorporated in the heat transfer coil of an outside condensing unit portion of a direct expansion air conditioning system, the present invention could also be advantageously utilized in other types of heat transfer coils, such as indoor evaporator coils in furnaces and heat pump units, if desired. Also, principles of the present invention could be advantageously utilized in flat coils, and coils which have a non-vertical orientation.